1. Field of the Invention
This invention relates to a copper alloy sheet useful as electronic parts and particularly, those parts such as terminals/connectors, switches, relays, lead frames and the like. The copper alloy sheet of the invention has excellent mechanical properties and electrical conductivity, and are thus suitable for the above purposes. In addition, the alloy sheet has a good stress relaxation resistance characteristic and good bend formability, enabling the alloy sheet to show better performance upon use as electronic parts, such as terminals/connectors, switches, relays, lead frames and the like, which are required to be down-sized and are placed in a high temperature environment.
2. Description of the Related Art
It has been hitherto employed, as electronic parts such as terminals/connectors, copper alloys including brass (C26000), phosphor bronzes (C5111, C5191, C5212, C5210), Cuxe2x80x94Snxe2x80x94Fexe2x80x94P alloy (C50715), and the like. In recent years, there have also been used copper alloys such as Cuxe2x80x94Nixe2x80x94Snxe2x80x94P alloys, Cuxe2x80x94Nixe2x80x94Sixe2x80x94Znxe2x80x94Sn (xe2x80x94Caxe2x80x94Pb) alloys, Cuxe2x80x94Nixe2x80x94Sixe2x80x94Mg (xe2x80x94Zn) and the like. Patent documents concerning copper alloys, which belong to alloys of the same type as the copper alloy sheet of the invention and contain Ni and Si, include, for example, Japanese Laid-open Patent Application Nos. Hei 9-209061, Hei 8-319527, Hei 8-225869, Hei 7-126779, Hei 7-90520, Hei 7-18356, Hei 6-184681, 6-145847, 6-41660, Hei 5-59468, Hei 2-66130 and Sho 61-250134, and Japanese Patent Publication No. Sho 62-31060.
With the recent development of electronics, electronics parts such as terminals and connectors tend to be down-sized, for which more improved reliability thereof has been demanded. This is illustrated using, for example, terminals used in the field of automobiles. For the purposes of insuring an accommodation space, improving accommodation properties, and shortage of transmission wires (to permit location of electronic appliances in the vicinity of an engine for engine control), electronic and electric appliances mounted in an engine room increase in number. The increase in number of appliances for electronic control and the increase in amount of transmission signals results in an increase in number of pins of wire harnesses. Nevertheless, it becomes necessary to arrange a junction block and a terminal box in a narrow space, thus contemplating fabrication of more down-sized and more lightweight connectors.
In such down-sized and lightweight connectors, processing techniques such as 180 degree bending at 0 radius and bending after notching (i.e. a bent portion is notched and then bent) as shown in FIG. 1 or xe2x80x9cnotchingxe2x80x9d have been adopted for the purpose of making up for the lowering of rigidity caused by reduction in sheet or plate thickness and also ensuring high dimensional accuracy. When subjected to such a processing technique, existing copper alloys undergo generation of fine cracks at the bent portion, thus leaving the problem that when the resultant terminal is employed, its reliability lowers considerably.
In the connection operation of connectors, an insertion force expressed as (initial contact force of connector) X (coefficient of friction at the time of insertion) X (pin number)is needed. If the initial contact forces of terminals are at the same level, the increase of the pin number results in an increasing insertion force. This is one of factors contributing to increasing the fatigue of workers who perform assembling operations. In order to suppress the insertion force from increasing after the increase in the pin number, it have become necessary to reduce the initial contact force of terminals substantially in reverse proportion to the increase in the pin number. However, when terminals are formed of a copper alloy material having the same stress relaxation rate, it is not possible to maintain a standard value of a contact force necessary for keeping the reliability for use as a terminal. This is because an initial contact force of a down-sized terminal having a large number of pins is set at a low level, thus exerting stress relaxation on the terminal as time goes. Hence, in order to keep a given contact force B necessary after passage of time, in terminals having a large number of pins, there is required a specific type of copper alloy material, which has a smaller initial contact force (Axe2x80x2 less than A) and a smaller degree of stress relaxation (Cxe2x80x2 less than C), i.e. a smaller stress relaxation rate (1-B/Axe2x80x2 less than 1-B/A) than those materials used as a terminal having an small number of pins. This is particularly shown in FIG. 2. In addition, such an alloy material should have high strength (yield strength) so that it can yield a substantial contact force on its use as a down-sized spring portion.
As will become apparent from the above, with the down-sizing of terminals, there are demanded copper alloy materials, which have better bend formability, stress relaxation resistance, and strength (yield strength) than existing copper alloys. Especially, with regard to the stress relaxation resistance characteristic, the higher performance of engines results in a higher temperature in an engine room. This strongly demands the development of copper alloys whose stress relaxation resistance is good at high temperatures exceeding 150xc2x0 C.
In order to meet the above demand, attempts have been made on the processing step of terminals/connectors with the use of combinations of soft copper/copper alloys having good electrical conductivity and formability or processability and stainless steel materials having good yield strength and formability along with a good stress relaxation resistance. This presents the problem that the processing steps are complicated with poor economy. On the other hand, hitherto employed copper alloys, respectively, have the following problems. Conductivity and stress relaxation resistance are poor for bronze and phosphor bronze, stress relaxation resistance is poor for Cuxe2x80x94Snxe2x80x94Fexe2x80x94P copper alloys, and yield strength is poor for Cuxe2x80x94Nixe2x80x94Snxe2x80x94P alloys. This is true of Cuxe2x80x94Nixe2x80x94Si alloys, e.g. Cu-2Ni-0.5Si-1Zn-0.5Sn(xe2x80x94Caxe2x80x94Pb) alloys are poor in formability and stress relaxation resistance, and Cu-3Ni-0.65Si-0.15Mg alloys are poor in formability.
It is accordingly an object of the invention to provide an alloy material which overcomes the problems of the prior art counterparts.
It is another object of the invention to provide an alloy material which has good yield strength, electrical conductivity and stress relaxation resistance characteristic along with good formability sufficient to ensure 180 degree bending at 0 radius, and thus is suitable for use as electronic parts such as terminals/connectors, lead frames and the like.
We made intensive studies on Cuxe2x80x94Nixe2x80x94Si alloys in order to solve the prior-art problems, and as a result, found that the above objects can be achieved by appropriately controlling the amounts of Ni, Si and Mg in Cu along with the amounts of Zn and Sn, if necessary, and also by appropriately controlling an average grain size of a product sheet and also a size of an intermetallic compound precipitate of Ni and Si.
More particularly, the invention contemplates to provide a copper alloy sheet which has good stress relaxation resistance and bend formability and is adapted for use as electronic parts, the copper alloy sheet comprising 0.4 to 2.5 wt % of Ni, 0.05 to 0.6 wt % of Si, 0.001 to 0.05 wt % of Mg, and the balance being Cu and inevitable impurities wherein an average grain size in the sheet is in the range of 3 to 20 xcexcm and a size of an intermetallic compound precipitate of Ni and Si is in the range of 0.3 xcexcm or below. The copper alloy sheet may further comprise 0.01 to 5 wt % of Zn and/or 0.01 to 0.3 wt % of Sn. If Sn is present, it is preferred that the following equation is satisfied when the content by wt % of Mg is represented by [Mg] and the content by wt % of Sn is by [Sn]
0.03xe2x89xa66[Mg]+[Sn]xe2x89xa60.3
Further, the copper alloy may further comprise 0.01 to 0.1 wt % of Mn and/or 0.001 to 0.1% of Cr. Separately, at least one of Be, Al, Ca, Ti, V, Fe, Co, Zr, Nb, Mo, Ag, In, Pb, Hf, Ta and B may be further contained in the alloy in a total amount of 1 wt % or below.
When the X-ray diffraction intensity from plane {200} in the sheet surface is taken as I{200}, the X-ray diffraction intensity from plane {311} is taken as I{311}, and the X-ray diffraction intensity from plane {220} is taken as I{220}, the following equation should preferably be satisfied
[I{200}+I{311}]/I{220}xe2x89xa70.5
In addition, It is preferred that the yield strength is 530 N/mm2 or above.